Homework Help:
Find the spring constant

A car with mass m rolls d down a frictionless [tex]\theta^0[/tex] degree incline. If there is a horizontal spring at the end of the incline, what spring constant is required to stop the car in a distance of x?

3. The attempt at a solution

[PLAIN]http://img4.imageshack.us/img4/8837/unledxrq.jpg [Broken]

I am honestly very embarrassed that I can't do these basica problems properly and I am a rising sophomore.

An object falls, an object is dropped, a car rolls down a hill, a block slides down a slope, ...

In all these cases the object is starting with zero velocity.

When the question starts

An object is thrown, A projectile is lauched, or similar, it is NOT starting with a velocity of Zero.

Actually "an object is dropped/falls" can be tricky, since it can sometimes be dropped/fall from a moving point - but then you will realise it is moving so it shouldn't be a problem.
Examples could be:
You dropped a book while in a lift traveling up at 2 m/s
A bomb falls from an airplane traveling at ......
A bag of nuts falls out of a roller coaster when it speeds over a crest ....